7. PROJECT SUMMARY/ABSTRACT The development of new medications to reduce the burden caused by opioid use disorder (OUD) is a high priority in addressing the opioid crisis. However, the currently available tools and endpoints to evaluate and approve new medications to treat opioid use is an impediment to medication development. Measures of change in the diagnostic criteria (i.e., symptoms) of OUD have rarely been used as indicators of improvement from treatment, despite this approach being standard practice for other psychiatric disorders. There is preliminary evidence from multiple clinical trials that change in Diagnostic and Statistical Manual of Mental Disorders (DSM) diagnostic threshold and criteria counts has potential utility as a clinically meaningful outcome. However, the only validated assessments for measuring the presence and severity of DSM-5 OUD are clinician-administered, semi-structured interviews, requiring extensive training and cost making them impractical for broad use. In this project, we propose to develop a new clinical outcome assessment that is an electronically-administered, patient self-report instrument directly linked to DSM-5 diagnostic criteria for measuring the severity of OUD, the ?Opioid Use Disorder Severity Scale? (OUDSS). The specific aims are to: (1) generate a pool of self-report items based on structured clinical interviews for OUD and existing items banks of substance use disorder severity to create an electronic, self-administered instrument directly linked to the diagnostic criteria in DSM-5; (2) evaluate the content validity and administration procedures of the OUDSS through one-on-one qualitative interviews with 20 patients with OUD; and (3) evaluate the reliability and validity of the OUDSS in a diverse sample of 300 individuals seeking/enrolled in outpatient treatment to determine construct validity, test-retest reliability, and ability to detect change. Development and evaluation of the OUDSS will follow the FDA Guidance for Patient Reported Outcome (PRO) measures. Because of the rigorous methods required for development of a PRO instrument, we are targeting OUD rather than general substance use disorders for development during the period of this award. As DSM-5 diagnostic criteria are equivalent across substances of abuse, the OUDSS could be modified for other specific substances (or substance use disorders in general) with minimal effort. A validated, easy to administer, electronic PRO measuring OUD severity would be a significant contribution to treatment research, clinical care, and medication development.